The present invention relates generally to semiconductor device fabrication and more particularly to forming contacts to circuit structures on a GaAs monolithic microwave integrated circuit (MMIC).
Various techniques, including wire-bonding and emerging flip-chip and TAB (Tape-Automated-Bonding) technology, have been utilized to form contacts with circuit structures on the front side of an MMIC.
Electrical interconnection between a wire-bonded MMIC and the next level of packaging, e.g., a printed circuit board (PCB) is accomplished using a plastic microcircuit package usually consisting of copper leads, multiple wire bonds, and an epoxy encapsulant. MMIC pads are connected internally to package leads with the wire bonds.
However, because of its complexity and unreliability wire-bonding is being replaced by new emerging technologies.
Typically, backside processing includes polishing to thin the substrate to several mils in thickness, the formation of via holes to connect to circuit structures on the front face to be grounded, e.g., the source terminal of an MESFET, and plating the back surface to form a ground plate.
In the case of emerging flip-chip technologies and concepts, the MMIC input/output pads on the front side of the substrate are plated with thick metalization, up to several hundred microns thick, to form bumps. These bumps on the MMIC are used to connect to the PCB by turning the device over (front side down) and soldering the bumps to the PCB conductors. The bumps must be heavily plated so active circuitry on the front side of the MMIC will not be damaged when the MMIC is mounted.
An important part of the manufacturing process is establishing Known Good Die (KGD). However, establishing KGD is problematic for Chip-on-Board (COB) technologies such as Flip-Chip-on-Board because functional testing must be carried out after the last process step is completed. Standard wafer probing equipment cannot be used with bump technologies to perform this functional testing because the bumps are very thick, rounded, and/or have geometry not conducive to standard wafer probing equipment. Accordingly, elaborate techniques such as placing die on a test board, soldering, testing, and then de-soldering have been established to solve the KGD problem for flip-chip mounted ICs.
Accordingly, there is a need for a contact technology to replace wire bonding that facilitates efficiently establishing KGD.